As an example of conventional roadside-to-vehicle communication systems, the standard “Dedicated Short-Range Communication (DSRC) System Standard ARIB STD-T75”, standardized on Sep. 6, 2001, which was established by Association of Radio Industries and Businesses, is known. The standard is to standardize a system for roadside-to-vehicle communications that is performed by means of spot communication whose communication zone is limited, and deals with multiple applications, utilizing an identifier referred to as AID for each application.
However, the foregoing conventional art in which base stations are always masters and mobile stations are always slaves can implement master-slave-type application only, thereby has not been able to be applied to such applications as activating communication or performing even communication between a mobile station and a base station. Moreover, the identifier referred to as AID can define 32 applications only; therefore, there has been a problem in that it is difficult to deal with applications when the kinds of applications increase. Furthermore, the size of data that can be transmit/received at a time is small, for example, about several hundreds of bytes; therefore, it has been difficult to apply the foregoing conventional art to applications that require high-capacity data communication with several tens of kilo bytes.
As an example of approaches to the solution for these problem, by placing Application Sub-layer Extended Link Control Protocol (ASL-ELCP), which is a protocol allowing bidirectional communication, on the foregoing standard (Dedicated Short-Range Communication (DSRC) System Standard ARIB STD-T75), thereby making a base station periodically poll a mobile station about whether there is any communication from the mobile station or not, communication from mobile stations is implemented.
In addition, by defining an identifier referred to as access-point identifier in Application Sub-layer Extended Link Control Protocol (ASL-ELCP), thereby allowing a plurality of protocols to operate on a layer that includes the foregoing standard (Dedicated Short-Range Communication (DSRC) System Standard ARIB STD-T75) and the foregoing Application Sub-layer Extended Link Control Protocol (ASL-ELCP), and by utilizing the Internet Protocol as one of the plurality of protocols, a countermeasure for the multiple applications is implemented. Moreover, by providing segmenting/assembling means referred to as bulk transfer, a message of up to about 50 kilobyte can be transmitted and received. Still moreover, in broadcast communication, by recurrently transmitting the same data multiple times, keeping the error rate of communication low is implemented (e.g., refer to Non-Patent Literature 1).
Non-Patent Literature 1:
The Information Processing Society of Japan, ITS study group, “Implementation and Evaluation of DSRC (ARIB STD-T75) system”, 2002-ITS-10-0.